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Generally, oviposition only follows a blood meal. For various reasons the interval between feeding and egg laying varies from five to 25 days, although (in tubes in jars with slightly moist cotton, maintained at 29.5°c. to 30°c.) the average is six to nine days (Jobling, and others). [ Specialists will be interested in Wigglesworth's (1943)_brief account of the fate of haemoglobin in ovipositing females.
As each egg is emitted from the female genital aperture it normally comes in contact with a peculiar glandular organ, gene's organ, that lies dorsally at the base of the capitulum. Gene's organ, which is everted only during oviposition, envelops each egg and provides it with a waxy, waterproof coating. Should this organ fail to evert or if any eggs are missed, these shrivel and fail to hatch, even in a humid atmosphere. The waxy coating is soft and viscuous (melting point 50°C. to 540C., in contrast to cuticular wax, which is hard and crystalline with a melting point of 6500.). The critical temperature of 0. moubata eggs well covered by this wax is 45oC. Lees and Beament (1948) have made a detailed study of gene's organ and its secretion, temperature and water loss of eggs, morphology of the female genital tract, structure and chemistry of the egg shell, and permeability of the egg shell.
Eggs are deposited in masses on the soil or in hollows burrowed out by the female. It has been stated that the masses are agglutinated. Actually, individual eggs have a somewhat adhesive coating. When a container in which they are kept is jostled they roll about like globules of mercury.
This is true also for eggs of numerous other argasids that have been observed.
After oviposition, the female "broods" over the eggs for some days (Wellman), a phenomenon of unknown function common among argasids. Jobling observed that this "brooding sometimes con tinues till the nymphal molt, after which the female may walk about for a time with several nymphs clinging to her.
Dutton and Todd recorded individual batches of ten to twenty eggs, with the greatest total of several batches from a single female numbering 139 eggs, Møllers (1907) observed a single batch of eighty eggs. Wellman mentioned a lifetime total of 88 eggs and Newstead reported a total of 94 eggs. Records obtained under opti. mum laboratory conditions have been higher than those secured by
these early field and laboratory workers, Cunliffe observed a female that produced a lifetime total of 535 eggs of which over ninety percent were fertile. In Jobling's tests, one female deposited several batches totalling 1,217 eggs and eight other females laid totals of from almost 700 to over 1000 each. Dr. G. E. Davis and Dr. W. Burgdorfer report (conversation) that the largest number of eggs they have observed in a single oviposition has been 233 and 327, respectively. Most eggs are laid at night and sometimes more than one day is necessary before a full batch is deposited.
Six or seven batches, gradually diminishing in numbers, appear to be usual in one female's lifetime. The amount of the previous blood meal influences the member of eggs subsequently produced. Jobling noted that the fertility of later batches de creases.
In a laboratory study of 0. moubata fertility, Robinson (19420) found that three egg batches may be laid after one mating but that egg fertility is considerably increased if mating occurs before each oviposition. Fertility decreases when the interval between mating and oviposition is extended. Oviposition occurs almost without exception only after a blood meal. Eggs show no alteration in fertility when maintained between 22°C, and 32°C., but at 34°C. no larvae emerge. [As already stated, Lees and Bean ment (1948) have stated that 450C. is the critical temperature for normal eggs.] Robinson recommenced a temperature of 30°c, and a relative humidity of 50% in the breeding chamber for safe and speedy production. He found that a female might deposit a few eggs without a blood meal and that large females produce more than do small ones. The range in number of eggs per female per batch in these experiments varied from fifty to 250, with an average of 170. Many females died shortly after their first blood meal; others after depositing their first egg batch,
According to Robinson, females lay over twice as many eggs when sand rather than a flat surface such as filter paper is pro vided for this purpose, but Dr. G. E. Davis and Dr. W. Burgdorfer report (conversation) that in their experience the opposite is true.
Figure 44, Egc just deposited
Figure 49, Rupture of egg shell Figure 45, Embryo, fourth day
Figure 50, Larva hatching Figure 46, Embryo, sixth seventh day Figure 51, Larva with shell, ventral view Figure 47, Hatching ege, lateral view Figure 52, The same, dorsal view Figure 48, The same, alternate contraction Figure 53, Larva, without shell, dorsal view and expansion
Figure 54, The same, ventral view
The egg of 0. moubata is among the largest known from ticks.
A newly laid egg (Figure 44) is slightly ovoid, glistening golden yellow, and measures approximately 0.9 x 0.8 mm. later it becomes reddish brown. Eggs from older females are light to dark brown in color. An irregular, faint, whitish, polygonal reticula tion and interrupted radiating streaks may be seen through the cuticle. The internal larva becomes discernable four days after the egg is deposited and occupies the whole egg by the sixth or seventh day (Figures 45 and 46). [ An alkaline haematin product originating from haemoglobin in the maternal blood meal has been demonstrated in eggs (Wigglesworth 1943). /
Eight days after the egg has been laid (temperature 3000.), the larva emerges by alternate contractions of the anterior and posterior ends of the body (Figures 47 and 48) that rupture the shell (Figure 49) and expose the larval dorsal surface. The shell may be completely detached in this manner, but usually remains on the ventral surface_covering the mouthparts and legs (Figures 50 to 54). [ Jobling_]
When movements necessary for emergence are completed, the larva becomes quiescent till the nymphal molt. That larvae are nonmotile after hatching and do not feed has been conclusively established for over a century, though several recent textbooks on medical entomology report differently. All observers have noted the quiescent stage between hatching and molting, and have differed only in the time required for a larva to molt to a nymph. Davis (1947) found that this molt occurred only a few hours after emer. gence from the egg. Robinson (1942) and Jobling stated that larvae molt four days after emerging from the egg (minimum, three days; maximum, five days). The various early observers reported periods of from three to 23 days from hatching till the nymphal molt.
[The sacculated gut of a newly hatched larva is filled with a reddish brown fluid (Wigglesworth 1943). The inference is that this is an alkaline haematin resulting from the ingestion of haemoglobin by the mother tick. ]
Before molting, the larva pales in color; its legs and mouth parts shrink. Its skin becomes detached from that of the internal
ORNITHOD OROS MOUBATA LARVAL-NYMPHAL MOLT
[ After Jobling (1925)
nymph; surface grooves disappear and the contour becomes more con vex. The internal nymphal outline and limbs are now visible. The two fore pairs of legs move to cause pressure on the larval skin resulting in a transverse rupture from which the anterior part of the body and the anterior legs emerge (Figure 55). After all legs are free, the larval skin is abandoned. [ Jobling ]
The nymphal stage, in contrast to the quiescent larval stage, is very active. Cunliffe observed four to eight nymphal instars